Nick Coghlan writes:
> On 15 April 2016 at 00:52, Stephen J. Turnbull <step...@xemacs.org> wrote:
> > Nick Coghlan writes:
> >
> > > The use case for returning bytes from __fspath__ is DirEntry, so you
> > > can write things like this in low level code:
> > >
> > > def myscandir(dirpath):
> > > for entry in os.scandir(dirpath):
> > > if entry.is_file():
> > > with open(entry) as f:
> > > # do something
> >
> > Excuse me, but that is *not* a use case for returning bytes from
> > DirEntry.__fspath__. open() is perfectly happy taking str (including
> > surrogate-encoded rawbytes).
>
> That results in a different type for the file object's name:
>
> >>> open("README.md").name
> 'README.md'
> >>> open(b"README.md").name
> b'README.md'
OK, you win, __fspath__ needs to be polymorphic.
But you've just shifted me to -1 on "os.fspath": it's an attractive
nuisance. EIBTI, applications and high-level library functions should
use os.fsdecode or os.fsencode. Functions that take a polymorphic
argument and want preserve type should invoke __fspath__ on the
argument. That will visually signal that the caller is not merely
low-level, but is explicitly a boundary function. (You could rename
the generic function as "os._fspath", I guess, but I *really* want to
deprecate calling the polymorphic version in user code. _fspath can
be added if experience shows that polymorphic usage is very desireable
outside the stdlib. This remark is in my not-so-Dutch opinion, of
course.)
> The guarantee we want to provide those folks is that if they're
> operating in the binary domain they'll stay there.
Et tu, Nick? "Guarantee"?! You can't guarantee any such thing with
an implicitly invoked polymorphic API like this one -- unless you
consider a crashed program to be in the binary domain. ;-) Note that
the current proposala don't even do that for the binary domain, only
for the text domain!
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